sorry, ca was meant to be ch-I haven't used bags of shock. The only things I have used is liquid shock, bleach and a chlorinator but not using chlorinator now. It's clearing up a little but I will maintain FC at shock level and yes I am going by best guess guide. Also when I back flush how much water is suppose to come out? It seems very little and wondering if it's working but I am getting good pressure when it's filtering. Could there be channeling going on?